HIGH EFFICIENCY DOWNDRAFT OVERVIEW
A downdraft table is used to collect dust from a specific operation such as sanding, grinding, polishing and welding. This type of equipment is classified as a pollution control device. The tables can be self contained or connected to a centralized dust collection system.
When a self contained downdraft table is energized, a motor and air mover rotate to produce air volume and create a negative atmosphere below the surface of the table.
The table top is typically slotted to allow dust to be drawn into a chamber where the dust is captured using some form of filter media. The filter media can be arraigned as static filtration or dynamic filtration.
In a static filter configuration, the filters are usually disposable. Obviously, this configuration is less expensive initially. A static filter configuration is usually a pleated panel type filter. Note that static filtration cannot be cleaned on-line. As time passes and the dust builds up on the filter surface, the air volume throughput is reduced proportionately.
In a dynamic filter configuration the filters are usually cylindrical cartridge type that are coupled to a continuous duty pulse jet cleaning system. Some filter cleaning systems are operator initiated. This type of filter can last a year or more. Some filters are washable.
A downdraft table comes configured in many sizes and performance ranges. The table must be selected based on the specific operation.
A simple formula can be used to determine the downdraft velocity of the air. Velocity = CFM/Area (sq.Ft.)
Example – 36” x 72” = 2592/144= 18 square feet. If the fan produces 2700 cfm at 4” wc of static pressure, the downdraft velocity is 150 feet per minute. Note the 4” of water column static pressure at the rated flow. The fans ability to overcome the resistance of the filter and associated dust cake is paramount to the performance of the table.
Typically a squirrel cage fan wheel is not suited for static pressures above 2” wc.
Caution must be excercised when using a table for metal work. Most dry filtration type downdraft tables are not suitable for combustible metal dusts. Please consult with our specialists to determine what type of system will be best suited for your application.
Call us to discuss your specific downdraft table equipment application needs.